As most people who have LiFePO4 batteries know, SOC is difficult to determine because of the very flat charge\discharge curve. To the degree that SOC can be estimated based on voltage, in order to have any hope of accuracy this must be resting voltage, where "resting" can mean anything from 4 to 12 hours.
Now suppose you have a LiFePO4 bank that you want to keep between 20% and 80% SOC to maximize cycle life. You run the batteries down to the point where the resting voltage matches 20% SOC. If you could now keep track of Ah into and out of the battery bank, and trigger events such as "stop charging" and "start charging" based on those values, wouldn't this be extremely useful to LiFePO4 owners?
Suppose you have a 100 Ah LiFePO4 bank. In this instance, starting at the known 20% SOC point, you'd set charging to stop when 60 Ah have gone into the bank, because this represents 80% SOC. Likewise, if the Ah ever goes into negative territory, you know you've dipped below 20% SOC, and you could use and AUX to trigger a relay to disconnect loads.
I may well be missing something, but it doesn't look to me like this is, um, currently (sorry) possible with the WBJr/Classic. Here's hoping I AM missing something!
I welcome any thoughts. THx.
Ideally, the interaction / interoperation with the BMS of the battery would be the best of all options and in several BMS' like Orion, Batrium, TinyBMS have Modbus, canbus or other methods & protocols to interact with them. I am also setting up to install a 24V/400AH lifepo pack which does not have a BMS that can be interacted with and this is an obvious concern for me as well. If I have to change the BMS, that's fine but from what I could find there is limits to what can be done with a Classic. If you have a Midnite Battery Monitor, that also won't be much use either for the lifepo because of how Lifepo discharges and it's voltage curve.
I had some LiFePo4 batteries and was using a top voltage where they should be at 80% and then used ending amps to go from absorb to float and was using bottom balancing. I think you would only need to be able to cut out batteries at a low voltage like a BMS does to prevent the batteries from being damaged.
I was not using BMS at the time - had a couple things I goofed up that a low voltage cutout would have helped - and it should be independent of the Classic .
At the time I got my batteries there weren't a lot of BMS or cell balancing products available - now there are lots of them.
Look in past forum discussions about bottom balancing and also Ross had mentioned something that balances the cells but is not really like a typical BMS.
Larry
Kind of highlights some issues here. Low Volt Cutoff is critical to keep the cells healthy & happy as much as high volt cut off. HI temp is an obvious must but in my case low temp sensing is also a must. It's -16c / 3F outside right now (-30c/-22F is not unusual) and IF I lost heat in my powerhouse it would be too cold to charge and if the batt's were freezing up and a charge is applied (bad things happen) I also get heatwaves in summer to 40c / 105F.
Case in point: On the 13th, our first real cold & snow fall, the small Furnace in the powerhouse failed. Luckily the thermal mass & hyper insulation prevented freeze up (my batteries, 50 gal water pressure tank are all in there) and I've been keeping it warm with a backup heater. Today's task is to replace it with another, so a $500 solution that could have cost several thousand very quickly. FYI: The building is only 14'x7' and I am using a small direct RV Furnace (12vdc, with own solar panel & battery) and LPG to maintain that building at this time.
Would really be nice if there was updates for LifePO and Li-Ion and a WizBang Senior or similar for Lithium which can interact with a BMS (cut offs etc). I "really" dislike mixing different products if I can avoid it... Much to be said for K.I.S.S. I had hoped that Midnite would have come up with their own LifePO Packs or small stackable ESS/HSS... Had also hoped they would have had an Inverter ready to go when I had to replace my 3kw one with a 4kw one.
Quote from: Steve_S on November 16, 2019, 05:22:44 AM
Kind of highlights some issues here. Low Volt Cutoff is critical to keep the cells healthy & happy as much as high volt cut off.
I'm of the old school that "an ounce of prevention is worth a pound of cure". LVD to me is an absolute, last-ditch effort. In 15 years off-grid, the only LVD events I've had have been from other people stupidity and refusal to follow stated procedures. (Long story I won't bother with right now). Since my family and I moved in, we have not had a single LVD event, ever. Because the system will kick in the generator long before that happens. And if for some reason the generator doesn't start, IT generates an alarm so we can intervene.
For a completely unattended site, or a site with zero technical capacity on site, LVD is probably a reasonable inclusion. For the rest of us, a properly designed and implemented system will never need it.
Quote
in my case low temp sensing is also a must. It's -16c / 3F outside right now (-30c/-22F is not unusual)
A civilised person such as myself would consider such environmental conditions "not fit for human habitation"!
I can't remember ever seeing less than -7C here, although we do get 48C and above in summer.
Ross, sounds like your in Australia or something. I am in North Eastern Ontario Canada near the Algonquin Park (easy to find on google map). Agreed that LVD is a last resort fail safe but it IS a fail safe. Yes, the Inverter (Samlex EVO) can start my generator and charge the batteries BUT Temperatures is another issue.
My old Yiyen Inverter had low volt cutoff & AGS (dip sw settings no software) and that would be too low (too low for FLA too) but that's a cheapo $600 USD jobby that is basic but works so you want to protect from equipment that isn't capable.
As for not having any and all "safeties" available is akin to the designers of the Titanic deciding to not have a lifeboat seat for everyone... nothing is ever 100% fool proof. 15 Years of IT Engineering for the Military, I can tell you about backups & triple redundancies and them still failing because of a single weak point or something stupidly omitted.
I have always been hoping that in a future Classic firmware they would add a batt temperature charge cutoff so we would have at least that layer of lithium cold weather charge protection. It could just be an Aux feature too.
Larry
TBH, I am actually very surprised that Midnite has not done more to accommodate LifePo & Lithium battery systems. The cost of LifePO versus FLA is now at the point where it's ridiculous to not go LifePO. Being in Canada and having temps like -18 this morning when I got up, low temp safeties are a must IF something goes awry.
Case in Point, the small furnace in my powerhouse packed it in on the 13th (of course it had to be on the 13th) while it was -16... Luckily I have manual backups and the new mini-furnace goers in tomorrow. My battery bank (still FLA, LifePo arrives Tuesday) was at 3 degrees before I found out the furnace quit.
I hope no one takes it wrong. I love my Classic, it's a great piece of kit BUT if I was starting out today and looking for gear, it wouldn't be a Midnite Classic simply because of it's inability to do some of the things other Quality products do. Gosh, even some of the Chinese "Value" gear does... I'm just hoping that SOON Midnite will come up with something to address the Battery Types & interacting with them as needed, otherwise I'll have to kludge something together, which is not my style.
Yes - a temperature cutoff would be a nice feature for a controller to have - for those of us in the cold country !
I guess we should get going on the Node Red project again since we can add all those features in pretty easily using the Classic battery temperature data via modbus.
Larry
Indeed, I intend to get back to my wee project sometime in December, too much todo right now and ol father winter is being generally a curmudgeon and quite hostile at this time.
I hope someone @ Midnite reads these posts and maybe can motivate some updates to 2020 realities.
Quote from: Steve_S on November 16, 2019, 05:46:49 PM
Indeed, I intend to get back to my wee project sometime in December, too much todo right now and ol father winter is being generally a curmudgeon and quite hostile at this time.
I hope someone @ Midnite reads these posts and maybe can motivate some updates to 2020 realities.
We are listening. We are also working on a lot of new things, including LiFePo stuff...
Not sure when something might change in the Classic though as our resources are kind of used up at the moment.
What features of other's products would help here ? From the first post, stopping charging at a maximum SOC seems like one feature ?
It's pretty much all software except for the BMS built into the battery system. A single board computer "could" handle all of that of course but I think you would like it done in the Classic.
Curious of some of the foreign controller features you like.
Really glad you're listening boB!
So...Hear Ye! Hear Ye!
When I had FLA I didn't pay much attention to WB Jr. net Ah, since voltage and SG together give a good read on SOC.
Now that I have LiFePO4, I'm convinced that TWO SIMPLE ENHANCEMENTS could HUGELY increase a Classic's functionality with these batteries. The most important rule LiFePO4 owners should adhere to (aside from temp constraints) is to keep depth of discharge between 20% and 80%. The super flat discharge curve makes voltage essentially useless for this purpose, at least on a daily basis. What voltage changes there are, are in the 10s of mV range. While the Classic can't see those differences, your BMS can. What to do? Simple: (1) calculate 60% of the bank's total Ah capacity; (2) carefully study the (resting!) voltage, as reported by your BMS, as you charge and discharge, so that you can (3) establish an accurate 20% or 80% SOC point, then (4) track net Ah.
HERE'S THE KEY: If you can configure the Classic to STOP CHARGING when net Ah reaches a specified positive value, you're preventing the bank from being over charged. If you can configure the Classic to TOGGLE AN AUX LOGIC LEVEL when net Ah reaches a specified negative value, you have a way to throw a contactor and disconnect some or all loads (but NOT the Classic!)
I know everyone at Midnite is maxed out. So many initiatives, so little time... But truly, these two changes in the software would go SO FAR toward accommodating the most critical needs of LiFePO4 owners. What can we do to entice you. Beer? A Home Depot gift certificate? Weekend for two at the world-famous Motel 6 in Peoria? A year's supply of blinker fluid and muffler bearing grease for your ride?
Thoughts? Thanks!
Quote from: openplanet on November 18, 2019, 12:42:26 PM
Really glad you're listening boB!
A year's supply of blinker fluid and muffler bearing grease for your ride?
Thoughts? Thanks!
Well, I don't drink (anymore) but maybe some blinker fluid might make me feel good.
Will chat with others about this but cannot guarantee any immediate action.
Over and out :)
Have been wanting the Classic to have a Rate Of Change of WB current as an additional means of ending Absorb, in addition to the present EA function.
Also, if the Jitter of the WB current could be reduced (further), this would be a large help for anything that uses WB currents.
boB, you are speaking of FirmWare enhancements, BUT, if we could ever see battery voltage Sense terminals on a Classic, that would be SO useful. Know that the new covey of MN CCs all seem to have this function, and adding hardware functions are probably not in the cards for Classics ...
If the rate-of-change in measured battery charge current function could be included in the FirmWare for the new CCs this would be a large plus, here.
FWIW, THANKS for asking, Vic
Yeah, you won't be seeing battery voltage sense on a Classic but the new stuff has it.
I would have liked to add V sense to the WB Jr. cuz it could have used the same communications wire method.
I don't think that there is actually any jitter in the WB Jr. values themselves. Just jitter in the Classic's charging during absorb at high input voltages.
Don't know if I remember hearing about SOC rate of change ? Sounds like an interesting idea though.
Thank you boB.
If the people you chat with need to chat with someone who can make a compelling, air-tight, overwhelming, stupendous, powerful, stunning, powerful case for these two enhancements, send 'em over to me and I'll work my persuasive magic. Oh, and did I mention that with these two enhancements sales of Classics will spike by at least 20%? Yup...
--Paul, aka Openplanet
Fair enough boB...but what about Net WbJr. Ah? As I tried in my last post to make the case, this alone would go a huge way toward enabling LiFePO4 owners to charge and discharge their battery banks in a way that protects them very effectively.
Can we hope for a firmware change that would let us toggle Aux outputs based on + and - Net Ah set points???
Been a while to get back to this thread.
Classic to LifePo issues. Not including the self-contained LFP packs which have their own internal BMS.
A Smarter BMS with the ability to communicate like http://chargery.com/BMS8T.asp (http://chargery.com/BMS8T.asp) or https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4 (https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4) as an example of TWO but there are many more is increasingly common, in addition to Separate Port BMS' which have an independent charging circuit aside from the load terminal.
Typical conditions to monitor for are:
- Hi & Lo temp to prevent charging in harmful conditions. Never charge below freezing or in over heat conditions.
- Hi & Lo voltage disconnect. Pretty obvious why, very voltage sensitive.
--- An AUX port being able to receive the ON/OF signalling from a BMS would save a LOT of hackery that is potentially more weak points in a system. more pieces subject to failure....
--- A simple 2 Stage Charging Profile to accommodate newer battery tech like LFP & LiIon. No need for Equalization...
Quote
boB
Yeah, you won't be seeing battery voltage sense on a Classic but the new stuff has it.
?? New Stuff ? Abandoning the Classic line or ??? Maybe time to get the pre-warranty end refresh of my C-200 if that's still going... Or is that like the free WizBangJr deal which never arrived ?
---- From Samlex: The Inverter I use, on their BMS interaction / capability. ------------------------------------
3.16 INSTALLING CONTROL INPUT WIRING FROM LITHIUM BATTERY MANAGEMENT SYSTEM (BMS) TO ENABLE / DISABLE CHARGING OR INVERTING Refer to Section 5.11.2 regarding “Stop Charging†or “Stop Inverting†protections for Lithium Ion Batteries when parameter “BATTERY TYPE†is programmed for Option 2 - “1=Lithium†(See programming details at Section 4.4.2.22.2 in the EVO-RC Manual attached at Appendix A)
The Battery Charger Section of EVO is designed to charge 3 types of batteries - Lead Acid / Nickel Zinc (Ni-Zn) / Lithium Ion. Lead Acid and Nickel Zinc (Ni-Zn) battery charging voltages are required to be compensated based on the temperature of the battery cells. Hence, Battery Temperature Sensor Model EVO-BCTS is required to be connected to the RJ-45 Jack (6, Fig 2.1) as explained at Section 3.15.
Charging voltages of Lithium Ion Battery are not affected by temperature and hence, Battery Temperature Sensor Model EVO-BCTS is NOT required to be used when Lithium Ion batteries are used. The RJ-45 Jack (6, Fig 2.1) can be used to feed control signals from certain Lithium Ion Battery Management Systems (BMS) that may have capability of enabling / disabling “Stop Charging†or “Stop Inverting†control signals for inverter chargers. This control signal is normally generated by the BMS by switching ON (enabling) or switching OFF (disabling) potential free, Drain (+) and Source (-) terminals of mini Opto Isolated Mosfet Switch [Solid-State Relay (SSR)]. Connect the control signal output from the BMS to RJ-45 Jack (6, Fig 2.1) as follows:
• BMS control signal terminal marked “+â€: o Connect to any of Pins 1/2/3/4 (Refer to Fig 3.13 for pinout of RJ-45 Jack. Pins 1 to 4 are internally shorted) • BMS control signal terminal marked “-â€: o Connect to any of Pins 5/6/7/8 (Refer to Fig 3.13 for pinout of RJ-45 Jack. Pins 5 to 8 internally shorted)
-------------------------------------------------------
Quote from: Steve_S on December 10, 2019, 01:49:38 PM
Been a while to get back to this thread.
Classic to LifePo issues. Not including the self-contained LFP packs which have their own internal BMS.
A Smarter BMS with the ability to communicate like http://chargery.com/BMS8T.asp (http://chargery.com/BMS8T.asp) or https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4 (https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36?category=4) as an example of TWO but there are many more is increasingly common, in addition to Separate Port BMS' which have an independent charging circuit aside from the load terminal.
Not familiar with these but may have a look. The guys working on the LiFePo batteries should definitely see those if they haven't already.
Quote
Typical conditions to monitor for are:
- Hi & Lo temp to prevent charging in harmful conditions. Never charge below freezing or in over heat conditions.
- Hi & Lo voltage disconnect. Pretty obvious why, very voltage sensitive.
There is a high temp turn-off already in the Classic but you might have to call tech support to find out how to change it. It involves getting into the modbus editor in the MNGP and changing one of the registers is all.
Low temp and Low voltage disconnect ? Not sure how important that is unless there is something really wrong with the batteries ? I might be brain dead right now and forgetting something important ? At low temperature, charging should heat the batteries up and low voltage should charge them up.
Quote
--- An AUX port being able to receive the ON/OF signalling from a BMS would save a LOT of hackery that is potentially more weak points in a system. more pieces subject to failure....
--- A simple 2 Stage Charging Profile to accommodate newer battery tech like LFP & LiIon. No need for Equalization...
Aux 2 can be programmed to turn on and off with a high or low logic signal. This mode was added to the Classic just for lithium BMS's actually. Can't remember who ?
Quote
boB
Yeah, you won't be seeing battery voltage sense on a Classic but the new stuff has it.
?? New Stuff ? Abandoning the Classic line or ??? Maybe time to get the pre-warranty end refresh of my C-200 if that's still going... Or is that like the free WizBangJr deal which never arrived ?
No, not abandoning the Classics. It'll be a little while before new CCs are out though.
Will have to see what the others have been doing. We have others around here that know way more than I do about this stuff anymore !
Quote
---- From Samlex: The Inverter I use, on their BMS interaction / capability. ------------------------------------
3.16 INSTALLING CONTROL INPUT WIRING FROM LITHIUM BATTERY MANAGEMENT SYSTEM (BMS) TO ENABLE / DISABLE CHARGING OR INVERTING Refer to Section 5.11.2 regarding “Stop Charging†or “Stop Inverting†protections for Lithium Ion Batteries when parameter “BATTERY TYPE†is programmed for Option 2 - “1=Lithium†(See programming details at Section 4.4.2.22.2 in the EVO-RC Manual attached at Appendix A)
The Battery Charger Section of EVO is designed to charge 3 types of batteries - Lead Acid / Nickel Zinc (Ni-Zn) / Lithium Ion. Lead Acid and Nickel Zinc (Ni-Zn) battery charging voltages are required to be compensated based on the temperature of the battery cells. Hence, Battery Temperature Sensor Model EVO-BCTS is required to be connected to the RJ-45 Jack (6, Fig 2.1) as explained at Section 3.15.
Charging voltages of Lithium Ion Battery are not affected by temperature and hence, Battery Temperature Sensor Model EVO-BCTS is NOT required to be used when Lithium Ion batteries are used. The RJ-45 Jack (6, Fig 2.1) can be used to feed control signals from certain Lithium Ion Battery Management Systems (BMS) that may have capability of enabling / disabling “Stop Charging†or “Stop Inverting†control signals for inverter chargers. This control signal is normally generated by the BMS by switching ON (enabling) or switching OFF (disabling) potential free, Drain (+) and Source (-) terminals of mini Opto Isolated Mosfet Switch [Solid-State Relay (SSR)]. Connect the control signal output from the BMS to RJ-45 Jack (6, Fig 2.1) as follows:
• BMS control signal terminal marked “+â€: o Connect to any of Pins 1/2/3/4 (Refer to Fig 3.13 for pinout of RJ-45 Jack. Pins 1 to 4 are internally shorted) • BMS control signal terminal marked “-â€: o Connect to any of Pins 5/6/7/8 (Refer to Fig 3.13 for pinout of RJ-45 Jack. Pins 5 to 8 internally shorted)
-------------------------------------------------------
Quote from: boB on December 11, 2019, 12:30:22 AM
..... Low temp and Low voltage disconnect ? Not sure how important that is unless there is something really wrong with the batteries ? I might be brain dead right now and forgetting something important ? At low temperature, charging should heat the batteries up and low voltage should charge them up.
Below 40F, Li batteries become less capable (charging & discharging) and below 33F unable to be safely charged.
Since their internal resistance is so low, there is very little self-heating, and off-grid usage doesnt usually charge/discharge hard enough to get them very warm, just a couple degrees above ambient.
Even here is NoCalif, winters get to 15F at 1500' elevation. A couple days of that and my NiFe bank is hovering around 32F, and I get condensation frost on my generator in the pole barn. I have to run 5-30 weight in the diesel to get it cranked, otherwise I can't spin it fast enough to start.
If I went to Li batteries they would be below 32 unless I had heaters on them. I use kerosene lamps in the pumphouse and greenhouse to keep the temps above freezing. So having a simple software tweak to inhibit charging below 33F would be beneficial immediately and solve the issue of the BMS disconnecting the batteries from the controller when cold
Charging below freezing 32F/0C with cannot be done without damage as Mike said. I'm in Northern Canada, -30 happens here and IF there is a heat failure in my powerhouse... safeties are important. Info on this forum and the main docs are minimal & what can be found not very helpful. The world moved beyond FLA
BTW: I promote the Classic as well as my Samlex Inverter because it is good gear and does what it should but without good documented features / functions that support LFP & LiIon & BMS interactivity it limits the potential.... Maybe it would be wise to pay attention to Victron & Others to see where they are a and how they are supporting LFP etc. Even an addendum that specifically addresses LFP & Lithium Variants and the settings etc (at minimum) for now woudl be better than what's available now...
@Mike: I use a propane furnace recovered out of a wrecked RV Camper... to keep my powerhouse / pumphouse warmed up, it's a Suburban brand, with a 12V & LPG, I have it running with the dual regulators, and a 12V battery attached to it's own Solar Charger to keep it independent. Quite convenient and much less fussy and without a pilot light, (electronic ignition) it works a treat.
Hi Steve, Just where are you north of the 49* Latitude?
I am in the Cariboo in BC. I like your use of a RV heater. How much insulation do you have (R value wise) and have you been successful at -40* ?
PS there was a post in your other thread I believe from a fellow at either CorMax or CMXbattery.com.
I went to their site and saw an interesting picture of their BMS... you might want to see if it does what you want.
I also have been discussing with a rep about a 500 Ah 24V unit.. LiFePO4 and they have addressed every question so far...
I'm near to CFB Petawawa (Algonquin Park) Ontario. Deep in the valley & up the line !
Powerhouse: the Powerhouse / Pumphouse 75' from cabin. It is heated via a small RV Furnace which I got from a wreck with electronic ignition, runs with 12VDC and has it's own AGM & Solar Panel with charger just for it. That building is also hyper insulated with 4" thick XPS between the studs (locally milled and really 2x4 not 1.5" x 3.5") and then 1" of XPS before exterior sheathing & cladding, it also has a frost protected slab foundation with radiant pex in it (for future). Th roof has 6" of PolyISO between the rafters and a cool roof system over it. The 1" creates a thermal break increasing R value. The XPS is R5 per inch, the ISO is R6 per inch. I keep the powerhouse at 10C because it also holds my 50 Gallon pressure tank & well head.
I bought a Chargery BMS8T with 2 300A relays and the relay delay board as well. This will allow me to hookup my RaspberryPi with NodeRed etc to communicate with the BMS as well as the Classic 200 & the Samlex EVO Inverter using Modbus. There is a thread on that.
OK on the low temperature cut-off for lithium. Like I said, I wasn't the expert.
It would seem to me that the BMS in lithium batteries should also take care of this issue but I guess that BMS's have a little ways to go yet.
So, is it unsafe to discharge them below freezing as well as charge them below freezing ?
You can discharge below freezing but not charge below freezing. BMS do handle Hi Temp, not all handle low temp or have low temp cutoff. The cutoff occurs @ the Battery / BMS meaning that is basically leaves a relay OPEN so the charge controller is feeding power to nothing ! (battery is essentially disconnected). SOME BMS' can & do use external relays which are in-line with the battery cable to disconnect the battery if triggered. -
In some cases, to disconnect solar charging, people are dropping the Solar Panel IN line before the charge controller. As well as other assorted means.
There are different types of BMS' with features & functions relative to their target market. Some are for E-Bikes and fairly basic, others for EV's are quite complex (as you all learned) then those for Energy Storage again are different with various features & functions. The "Basics" like charging profiles for LiIOn and LiFEpo4 (they are different), Hi / Lo Volt, Hi / Lo Temp need to be observed. for SOC / DOD measurements, very accurate voltage readings need to be monitored as well, there is very little "grace" there, unlike FLA and variants. An extra volt over full charge on FLA won't bother it but could be a problem for LFP / LiIon because often the DOD is user limited to 80/20. Meaning 80% full to 20% remaining and they operate their battery pack between those % for DOD to extend / prolong the lifespan of their batteries.
Yeah, the different chemistry or "alloys" maybe they should be called for lithium have different requirements for sure.
As for the relay being open (FETs usually these days), the BMS can tell when it is being charged or discharged so maybe that should be included ?
What they could do to help this maybe is to let the current go slightly into charge and for a certain amount of time (seconds or minutes) and THEN shut off the relay FETs for some amount of time and then turn them back on again.
This can be tailored to any lithium chemistry as needed.
The problem is, charge rate needs to be about c/100 at cold temps, so really, not worth charging at all. simpler to just not charge
The BMS preserves the battery when activated, by cutting the power lead, and now the charge controller has 103V of PV on it's input, and no battery connected.
So really, the Charge Controller needs the BTS to be able to inhibit charging below 33F
Couldn't this be a new menu item in the classic firmware, if BTS <33F , go to Resting mode ? Maybe in the temp comp selection menu ?
Does anyone know how Tesla deals with charging their car batteries when they are below freezing ? Do they have some resistance heating coils in the battery bank ? Or do they do a slow charge to gradually warm them up enough above freezing ?
Larry
There is a heating element in the coolant lines,
i feel too midnite classic missed the bus on lifepo4/lithium ion batteries. maybe it is just american conservatism. but it seems to me lead acid will soon be a thing of the past.
it seems to me midnite classic never much experimented with lifepo4 batteries. the experimenting was all done by users.
it seems to me midnite classic sort of abandoned the classic chargers for new things that seem not to appear anytime soon.
would have been better working with a reliable inverter manufacturer. (or bms manufacturer)
just saying
The majority of the Classic was done before Lithium batteries became affordable. Lead acid is still king of off grid systems because of price.
A properly designed BMS, (which all Li batteries should have,) allows the Classic work just fine with LiFePo4 batteries.
Many others are using them now with Li technology and are working.
Sure, there could be other features added to help out but how can we do that ?
It's hard enough to find people here that have the knowledge to do such engineering without having to raise the price prohibitively high amounts to justify the work. As it is, I am working 7 days a week and today.
AND we had to spend quite a bit on Australia only requirements on the Classic.
You should come up some time and we will give you the grand tour and show you how our resources are being used and why it is not as simple to do what you are asking for as quickly as you (or we) would like.
Something like stopping charging at low temperatures could be added fairly easily. After making any changes to CC code, the product has to go through a lot of testing to make sure that no new bugs have been added. That is another reason it is not as easy you one might think to add features.
thanks Bob for responding,
i can totally see your point. the midnite classic is a first class product.
might pick you up on your invitation, maybe in 1,5 years or so.
thanks again for telling us how it looks like from your side.
greetings urs
Quote from: australsolarier on December 25, 2019, 10:56:12 PM
thanks Bob for responding,
i can totally see your point. the midnite classic is a first class product.
might pick you up on your invitation, maybe in 1,5 years or so.
thanks again for telling us how it looks like from your side.
greetings urs
Thank you !
Would be great to have you up here when it's convenient !
Until then, enjoy your "warm" Christmas !
I would like to strongly recommend that this article be read when contemplating how to address LFP & Lithium Ion Batteries and what the Big Deal is... it is all well explained and covered here. Below is a couple of extracts to highlight the issues which require consideration.
https://marinehowto.com/lifepo4-batteries-on-boats/
Quote
MISLEADING or UNCLEAR MARKETING FROM CHARGE SOURCE MANUFACTURERS:
Unfortunately most commercially available chargers, solar controllers and alternator regulators are of extremely limited design and are just not well suited to charging LFP banks. Many of the charger manufacturers have no actual experience with LFP yet they have no qualms making up “Li-Ion†charge profiles. In short, many of the LFP charging schemes may be damaging to your cells over the long haul and you may not see rated cycle life.
PLEASE DIG DEEPER WHEN A CHARGER MANUFACTURER CLAIMS A “LITHIUM-ION†CHARGE PROFILE
Many of these profiles I’ve seen can damage your very expensive LFP bank. A charger that immediately comes to mind, with a Li-Ion setting of 14.6V absorption and a 14.4V float! 14.4V float!!!
Technically 14.4V / 3.6VPC or 14.6V/3.65VPC can be safe if charging stops entirely when 100% SOC is achieved and all the cells stay in perfect balance way into the upper knee. The concern here is that this particular charger uses a bulk duration multiplied by X type of algorithm to help determine the absorption voltage duration. This is a lead acid algorithm. This type of algorithm sets or extends the absorption duration based on the length of the bulk stage. Short Bulk = Short Absorption & Long Bulk (eg: LFP) = Long Absorption. Long absorption with LFP = NOT HEALTHY
Seeing as bulk charging is very long with LFP how long do you think the LFP absorption duration will be? Holding these cells at 14.4V indefinitely (float) is well…. As Homer Simpson says. D’oh…….. Again, please do your research on how a charger operates before using it with your expensive new LiFePO4 batteries.
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These chargers lack the ability to shorten the absorption voltage duration to be suitable for LFP.
Where these chargers also fall flat, as most lead acid chargers do, is in the lack of a dedicated voltage sense lead. Also the largest charger they make is just 60A. Kind of small for an typical LFP bank on a cruising boat. For an AC charger, a fully programmable unit is better. By fully programmable, I mean absorption duration (settable from 0 minutes to 30 minutes or anywhere in-between), voltage fully adjustable and FLOAT SET TO OFF or below 3.40VPC. In most cases the best unit for LFP will be a fully programmable inverter/charger.
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Dedicated Voltage Sensing Rant:
Here we go again.. In a nut shell there are very, very few chargers or inverter/chargers out there that offer dedicated voltage sensing. This is really quite pathetic. Sadly the charging portion of most inverter/chargers is apparently an after thought for the engineers who design them. The engineers who fail to provide dedicated voltage sense leads, on battery chargers or inverter/chargers, have failed you, the customer, when you’re seeking fast charging performance..
Who are these failures?
Mastervolt â€" No dedicated voltage sensing
Magnum â€" No dedicated voltage sensing
Xantrex â€" No dedicated voltage sensing
Which manufacturers actually care about battery charging performance?
Victron â€" Victron I/C’s have dedicated voltage sense terminals right on the main unit. Kudos to Victron!!
Outback â€" Can be done but requires FLEXNET DC & MATE Remote Control.
This is not to say Victron makes the best inverter/chargers but God damn if their engineers actually understand charging. Battery charging that is. (wink)
Follow me on this. No matter how big you size the wire for with a 130A+ inverter/charger you will still have some voltage drop between the charger and the physical battery terminals. Most charger manuals only account for wiring voltage drop but we should remember that each termination, busbar, shunt, fuse, battery switch etc. results in even more voltage drop. It is not uncommon to see 0.4V -0.8V of drop, at full charging output, even on factory installed inverter/chargers. While the I/C makers often insist you keep the unit 5′ from the batteries, this is not always possible on a boat.
In the real world, voltage drop happens, and is simply a fact of life.
How do we fix that?
Simple, dedicated non current carrying voltage sensing leads connected directly to the battery terminals so the charger can compensate for slight voltage drops in the system wiring and not enter absorption or the voltage limited charging stage prematurely.
when I had my lifepo4 batteries I had the classic set up to get to certain voltage but then cut off at an ending amps. The result was it would go from absorb to float in a very short time.
Larry
Quote from: ClassicCrazy on December 28, 2019, 10:28:39 AM
when I had my lifepo4 batteries I had the classic set up to get to certain voltage but then cut off at an ending amps. The result was it would go from absorb to float in a very short time.
Larry
I would love to see a graph of battery current vs. time for this for LiFePo4 batteries. With a very low cut off current for starters to see how the current drops off with time at a steady voltage.
Of course, I could just Google for this maybe ?
Quote from: boB on December 28, 2019, 06:22:06 PM
Quote from: ClassicCrazy on December 28, 2019, 10:28:39 AM
when I had my lifepo4 batteries I had the classic set up to get to certain voltage but then cut off at an ending amps. The result was it would go from absorb to float in a very short time.
Larry
I would love to see a graph of battery current vs. time for this for LiFePo4 batteries. With a very low cut off current for starters to see how the current drops off with time at a steady voltage.
Of course, I could just Google for this maybe ?
Bob there was a previous discussion a few years back by a guy who had 24v worth of 100 ah Calb batteries ( 16 cells) . He was doing bottom balancing so drained them to just about empty to get them all level on the bottom voltage. Then the theory is you fill them up to like 95% and it doesn't matter if the voltages are not exactly even at that point - and you don't loose much capacity because the last 5% takes a long time to charge . He didn't use a BMS . I tried doing that - but goofed up a few times cause I didn't know what I was doing and took my batteries down too low - I should have had a low voltage cutoff.
From what I remember the ending amps was 5 amps . I would have to look up what the other voltages were set for. Probably something like absorb of 3.5v per cell instead of 3.6 . And the float was low enough not to keep charging them.
Larry
ending amps should be in the specifications of the battery, in my case 0.02C
you cannot charge a lifep4 only to 80%, at least not for a longish period.
for various reasons bottom balancing is not practical. ( but discussion about it gets very heated)
i set absorb to 3,5V and float to 3.35V, but you can go a few decimals lower
a bms (balancing and cutoffs is a must)
12V banks keep much more balanced (have on that keeps balanced for years) than a 48v battery bank
high currents unbalance more (there are small resistances on the battery terminals and naturally more discharge/charge)
i am suggesting experimenting with lithium batteries is not a good thing at all.